The present invention relates to a fuel cell power generation equipment comprising an anode, an electrolyte membrane, a cathode and a diffusion layer, wherein fuel is oxidized at an anode and oxygen is reduced at a cathode, in particular, compact type portable power source using liquid fuel such as methanol as a fuel and mobile electronic devices using this power source.
Recent progress in electronics technology has contributed to miniaturizations of telephone set, notebook type personal computer, audio visual devices or mobile information terminal devices, and their use is increasingly prevailing as portable electronics devices.
Heretofore, these portable electronics devices were driven by a secondary battery, and have been developed through the appearances of new type secondary batteries from sealed lead battery to Ni/Cd, Ni/hydrogen and further Li ion batteries, and modifications to more compact and light weight types and higher energy density types. In any of these secondary batteries, cell active materials to enhance an energy density or cell structure having a higher capacity have been developed and efforts have been paid to obtain a power source with longer service time per one charge.
However, secondary batteries still have many problems for a long continuous drive of portable electronics devices because charging is indispensable after consuming a certain amount of power, and a charging equipment and a relatively longer charge time are required. Now, portable electronics devices are progressing towards devices requiring a power source enabling to supply a higher output density and a higher energy density, that is, a power source with a longer continuous service time, in response to an increasing volume of information and a higher communication speed in the future. Therefore, a need for a compact power generator (a micro power generator) serviceable without charging has been heightened.
As a power source responding to such requirement, a fuel cell power source is considered. Since a fuel cell directly converts electrochemically a chemical energy of fuel to an electric energy and does not require a driving unit like in a power generator using an internal combustion engine such as a usual engine-driven generator, its realization as a compact power generator device is highly possible. A fuel cell also does not require to temporary stop an operation of equipment for charging as in a usual secondary battery, because it can continue a power generation so long as a fuel is supplied.
For these requirements, a solid polymer type of fuel cell (PEFC: Polymer Electrolyte Fuel Cell) is known as a battery with a high output density, which generates power by oxidizing hydrogen gas at an anode and reducing oxygen at a cathode using an electrolyte membrane made of a perfluorocarbon sulfonic acid based resin.
To further miniaturize this fuel cell, for example, as disclosed in JP-A-9-223507, a compact type of PEFC power generation equipment has been proposed, in which cylindrical batteries equipped with anode and cathode electrodes at inner and outer surfaces of hollow fiber type electrolyte are assembled, and hydrogen gas and air are fed to inner and outer parts of the cylinder, respectively. However, in the application to a power source for portable electronics devices, a large volume of fuel tank should be provided due to a lower volume energy density of a fuel because the fuel used is hydrogen gas.
This system also requires auxiliary equipment such as an equipment to feed a fuel gas or an oxidizing gent gas (such as air) to a power generation equipment or to humidify electrolyte membrane to maintain the cell performance, which complicates a composition of power generation system and thus the system is not sufficient to attain miniaturization.
In order to raise a volume energy density of fuel, it is effective to use a liquid fuel and to eliminate auxiliary equipment to feed a fuel or an oxidizing agent to cell to obtain a simple composition. Such example has been proposed in JP-A-2000-268835 and JP-A-2000-268836, disclosing a direct type methanol fuel cell (DMFC: Direct Methanol Fuel Cell) using methanol and water as fuels.
This power generation equipment has an anode which is arranged in a manner to contact with outer wall side of a liquid fuel container via a material to feed liquid fuel by a capillary force, and is further composed of a solid polymer electrolyte membrane and a cathode connected sequentially.
This type of power generating equipment features in a simple composition not to require any auxiliary equipment to feed a fuel and an oxidizing agent thanks to a diffusive feed of oxygen to outer surface of a cathode which is exposed to ambient air, and also in a requirement for an electrical connection only without any separator as a connecting part for unit cells when multiple cells are combined in series.
However, since an output voltage per unit cell of DMFC under load is 0.3 to 0.4 V, DMFC requires a connection of cells in series by using multiple fuel tanks attached to a fuel cell to respond to a voltage required by portable electronics. Miniaturization of power generation equipment also requires increased number of cells in series and reduction of a fuel container volume per unit cell, remaining a problem that fuel container is divided into multiple containers in response to a number of cells in series.
In addition, a continuous service becomes difficult unless some discharging mechanism is realized for a gas generated in a liquid fuel tank by an oxidation reaction at an anode with an operation of this acid type electrolyte fuel cell.
An object of the present invention is to provide a fuel cell power generation equipment easily and continuously serviceable by feeding a fuel, without charging after consumption of a certain amount of power like a secondary battery, and a system using a fuel having a high volume energy density.
Another object of the present invention is to provide a compact power source most suitable for portable use as well as portable electronics devices using the same, wherein a fuel cell power generation equipment is composed of unit cells comprising an anode, an electrolyte membrane and a cathode laminated with a separator having a conductive fluid channel structure in between to obtain a specified voltage, the power source being a compact fuel cell without having an auxiliary equipment such as a fluid feeding mechanism instead of a conventional fuel cell having a fluid feeding mechanism which enforces passing through of a fuel and an oxidizing agent gas, enabling feeding a liquid fuel to each unit cell in any position of power source, and having a discharging function for a gas oxidized and generated in an anode from a fuel container.